Schistidium apocarpum
Schistidium frigidum
schistidium moss
frigid grimmia, frigid schistidium
1.2–12 cm, central strand weak or absent.
1–2(–4) cm, central strand distinct or absent.
erect or curved, rarely (falcate-) secund when dry, ovate-lanceolate, sharply keeled distally, (1.3–)1.7–2.5(–3.2) mm, 1-stratose or rarely 2-stratose in striae distally;
margins usually recurved throughout or to just before the apex, usually denticulate distally, 1 or 2-stratose;
apices acute or sub-obtuse;
costa percurrent or excurrent as a smooth or weakly denticulate, occasionally decurrent awn, abaxial surface often papillose;
basal marginal cells usually quadrate;
distal laminal cells mostly short-rectangular, 8–10 µm wide, smooth, sinuose.
erect or slightly curved, usually imbricate when dry, narrowly ovate-lanceolate to ovate-lanceolate, sharply keeled distally, 1.1–2.1 mm, 1-stratose, rarely with 2-stratose striae distally;
margins recurved to just before the apex, often denticulate distally, 1- or 2-stratose;
apices acute or somewhat obtuse;
costa excurrent as a coarsely denticulate, often slightly flexuose, usually decurrent awn, rarely percurrent (in alpine habitats), smooth;
some basal cells sometimes much lighter than adjacent cells, often hyaline, sometimes with yellowish walls, marginal cells quadrate or elongate-rectangular, often strongly trigonous or with more thickened transverse walls;
distal cells often of various shapes, short-rectangular or isodiametric, sometimes ovate or subtriangular, 6–10 µm wide, usually strongly sinuose.
autoicous.
autoicous.
dark red or brown, short-cylindric, 0.7–1.3 mm;
exothecial cells usually quadrate, sometimes mixed with short-elongate or oblate cells, thin-walled, usually trigonous;
stomata present;
peristome patent or erect, often twisted, 350–600(–700) µm, red, densely papillose, usually perforated.
red-brown, sometimes orange-brown, cylindric, 0.7–1.1 mm;
exothecial cells irregularly shaped, isodiametric or oblate, thin-walled or slightly thickened, trigonous;
stomata present;
peristome patent to squarrose, sometimes revolute, 230–300 µm, orange-red or yellowish red, densely to finely papillose, weakly perforated.
11–14(–19) µm, granulose or smooth.
10–14 µm, granulose or nearly smooth.
Schistidium apocarpum
Schistidium frigidum
Although H. H. Blom (1996) considered Schistidium apocarpum to be restricted in the flora area to the eastern portions of North America, it is more widespread and scattered across the continent. The denticulate leaf margins, papillose abaxial costal surface, short-cylindrical capsules, and the thin-walled, often evenly quadrate exothecial cells are distinguishing characters. The long peristome teeth are also useful in identifying S. apocarpum. In good condition the peristome can only be confused with that of S. trichodon, which differs in the darker, often black color of its plants, the peristome teeth often forming a dome, and the cylindrical capsules that retain the columella.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Schistidium frigidum is rather common yet is one of the more difficult taxa to determine with confidence, as the examination of many leaves is often necessary before the elongate basal marginal cells are obvious. Often, some central basal cells are much lighter than adjacent cells, and are often hyaline, and form contrasting patches, which helps to identify the species. In contrast to S. dupretii and S. confertum, which have a large proportion of elongate exothecial cells, S. frigidum has exothecial cells that are mainly isodiametric or oblate.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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